Conventionally, aluminum nitride sintered bodies have been used for circuit substrates and the like because they have high thermal conductivity and a thermal expansion coefficient relatively close to that of silicon. In recent years, the use of aluminum nitride has been proposed for heaters for semiconductor wafers used to form conductive films, insulative films, and resist films on semiconductor wafers and for etching semiconductor wafers as well as for inspecting semiconductor wafers. In these applications, the temperature distribution of the semiconductor wafer has a significant effect on product characteristics, resulting in a requirement that the temperature distribution on the semiconductor wafer surface be as uniform as possible. Thus, aluminum nitride, which has a relatively high thermal conductivity, is used.
For example, in Japanese Laid-Open Patent Publication Number Hei 11-74064, a metal paste such as tungsten or molybdenum is applied through screen-printing to serve as a resistance heating body on ceramics such as aluminum nitride. This is then sintered to provide a wafer heating device with an embedded resistance heating body.
In this type of wafer heating device, the metal paste is screen-printed on ceramics to serve as a resistance heating body, but pores and the like on the ceramics surface can cause pattern smearing and pinhole formation during printing. Also, when pores are present in the ceramics, they can hinder the transmission of heat from the resistance heating body to the wafer mounting surface, reducing the uniformity of the temperature distribution of the wafer.